The Christians follow the Bible as their sole holy book, and believe that there are no more legitimate prophets after the writing of Revelations (in fact, the more literally-minded ones treat the arrival of a "False Prophet" as a sign of the Apocalypse).

The Mormons have two holy books, the Bible, and the Book of Mormon, and believe that there were two more prophets, being two of their founding members: John Smith and Brigham Young.

Also, christians don't necessarily believe that there are no more prophets and that the bible is the only scripture. Most do, but it's not a requirement of being a christian. Mormons are christians. Obviously there are some differences otherwise they wouldn't be mormons.

Islam is more of a branch from Judaism than it is from Christianity. Jesus does exist in Islam, that is true, but they needed him to attract former Christians. Aside from the presence of Christ, Islam really has nothing to do with Christianity and take much more from Judaism. Which is ******* hilarious when you stop to think how much they hate each other.